It is known to lubricate mechanical devices such as driveline power transmitting devices, internal combustion engines or hydraulic systems with a lubricant comprising a polyoxyalkylene polyol oil of lubricating viscosity. However, due to the polarity of polyalkylene glycol fluids, difficulties have arisen utilising fully formulated lubricants, for instance the ability to prepare multi-grade lubricants.
In addition driveline power transmitting devices such as gears or transmissions, especially axle fluids and manual transmission fluids (MTFs), present highly challenging technological problems and solutions for satisfying the multiple and often conflicting lubricating requirements, whilst providing at least one of wear performance, durability and fuel economy. One of the important parameters influencing performance is lubricant viscosity and whether mono-grade or multi-grade lubricant fluids are useful for control of low temperature viscometrics and/or high temperature viscometrics. Lubricants capable of performing at lower viscosity typically provide increased fuel economy (thus improving CAFÉ efficiency). Conversely, lower viscosity fluids also contribute to elevated gear and transmission operating temperatures, which are believed to reduce fuel economy. Additionally, increasing lubricant viscosity is believed to provide better wear protection and durability to gears and transmissions.
Consequently, it would be desirable to provide a correctly balanced lubricant composition to meet the needs of mechanical devices such as gears and transmissions.
The lubricating composition of the invention is capable of imparting at least one of acceptable low temperature viscometrics, acceptable high temperature viscometrics, viscosity index (VI), oil blend thickening capabilities, shear stability, an acceptable co-efficient of friction, reduced operating temperatures, acceptable wear performance, acceptable corrosion, acceptable oxidative degradation, acceptable durability, or acceptable fuel economy.
U.S. Pat. No. 4,370,247 and European Patent Application 460 317 disclose polyalkylene glycol lubricating compositions.
U.S. Pat. No. 4,370,247 discloses the use of a polyalkylene glycol to reduce power loss due to a frictional decrease.
European Patent Application 460 317 discloses gear oil a lubricating composition containing a polyalkylene glycol lubricant and at least one sulphur-containing antiwear or extreme pressure agent. The gear oil lubricating composition does not include viscosity modifiers.